Bond pad having vias usable with antifuse process technology

ABSTRACT

A lower metal plate having a strip-like opening is used in a bond pad structure having metal plugs coupling the lower metal plate to an upper metal plate. A volume of relatively rigid material filling a volume above the strip-like opening transfers stress from the upper metal plate, through the strip-like opening, and to a foundation layer upon which the lower metal plate is disposed. The bond pad structure can be fabricated using the same semiconductor processing steps used to fabricate amorphous silicon antifuse structures having metal plugs.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.08/350,865, filed Dec. 7, 1994, entitled “Bond Pad Having Vias UsableWith Antifuse Process Technology” now U.S. Pat. No. 6,300,688 B1.

FIELD OF THE INVENTION

This invention relates to bond pads.

BACKGROUND INFORMATION

FIG. 1 (Prior Art) is a cross-sectional diagram of a bond pad structure.A layer of metal is deposited on a layer of oxide 2 and the metal isformed into a first metal plate 1. Metal plate 1 has a square shape whenviewed from a top-down perspective. As illustrated, a semiconductorsubstrate 3 underlies oxide layer 2. After formation of first metalplate 1, a second layer of oxide 4 is deposited over the entire die. Anopening is then formed in oxide layer 4 down to first metal plate 1 anda second layer of metal is deposited over the entire die. The secondlayer of metal is then formed into a second metal plate 5 which also hasa square shape when viewed from a top-down perspective. The entire dieis then covered with passivation 6. An opening is then formed throughpassivation 6 in the pad area to expose an upper surface of second metalplate 5. The second layer of oxide 4 of the bond pad structure is thelayer of oxide which typically separates a first layer of metal routingleads from an overlying second layer of metal routing leads elsewhere onthe die. First metal plate 1 may be connected to other circuitryelsewhere on the die via signal routing leads (not shown) formed of thesame first layer of metal that the first metal plate 1 is formed.Similarly, second metal plate 5 may be connected to other circuity viaother signal routing leads (not shown) formed of the same second layerof metal that the second metal plate 5 is formed.

During packaging, one end 8 of a bond wire 7 is attached to the secondmetal plate 5 and the other end of the bond wire is attached to a leadframe (not shown). End 8 is called a bond ball. The die, bond wires, andlead frame are then encapsulated in plastic to form the integratedcircuit package. As the plastic of the package cools it solidifies itshrinks. Because the bond wires (and the bond balls) are encapsulated inthe shrinking plastic, the shrinkage of the plastic with respect to thedie is manifest as a force on the bond balls inward toward the center ofthe die. A stress, indicated in FIG. 1 by arrows A, is therefore inducedin the bond pad structure. Plates 1 and 5 which are made of relativelysoft metal satisfactorily transfer the stress from the bond ball 8 tothe relatively rigid oxide layer 2 which in turn transfers the stress tothe underlying rigid semiconductor substrate 3.

FIG. 2 (Prior Art) is a cross-sectional diagram of a metal-to-metalamorphous silicon antifuse structure 9 and another bond pad structure.An amorphous silicon feature 10 of antifuse 9, when unprogrammed, has ahigh resistance which leaves a first signal routing lead 11 formed ofthe first metal layer essentially electrically isolated from a secondsignal routing lead 12 formed of the second metal layer. Antifuse 9 can,however, be programmed to form a permanent low resistance electricalconnection between the first signal routing lead 11 and the secondsignal routing lead 12. Programming is accomplished by flowing asuitable programming current through the amorphous silicon feature 10such that a conductive filament is formed through the amorphous siliconfeature 10 thereby connecting the second routing lead 12 to a conductivetungsten plug 13 of the antifuse structure. An electrical connection istherefore formed from the first signal routing lead 11, through thetungsten plug 13, through the filament in the amorphous silicon feature10, and to the second routing lead 12.

To make the amorphous silicon antifuse structure 9, oxide 4 is depositedand then a via is formed through the oxide 4 down to the first signalrouting lead 11. Tungsten is then blanket chemical vapor deposited (CVD)over the entire surface of the die so that tungsten fills the via andmakes contact with the first signal routing lead 11. The CVD tungstendeposits on all surfaces so that the via fills from the bottom andsides. As the tungsten is deposited in the minimum sized via, thetungsten deposited on the sidewalls of the via meets and completelyfills the via. Thus, as the tungsten deposition process continues, thetungsten deposits on top of the filled via resulting in a somewhatplanar surface. The tungsten is then reactive ion etched (RIE) back tothe upper surface of oxide 4. The RIE etchback removes a layer oftungsten from the non-via area and from the via area. However, becausethe vertical thickness of the tungsten in the via area is much thickerdue to the sidewall deposition, a plug of tungsten is left in the via.After tungsten etching, a chemical/mechanical polishing process is usedto planarize an upper surface of oxide 4 and tungsten plug 13. A layerof amorphous silicon is then deposited onto this planar surface andetched to form an oversized version of silicon feature 10. A secondmetal layer is then deposited and formed into second signal routing lead12. The oversized amorphous silicon feature is then etched to form thestack of the second metal routing 12 and the amorphous silicon feature10.

Due to the tungsten deposition and etch process, it is generally notdesirable to have a large via in oxide 4. The tungsten deposited on thevia sidewalls cannot meet in the center of a large via. A thin portionof tungsten will therefore be left in the center of the via. Duringtungsten etchback, the thin center portion of tungsten will be removedleaving only a tungsten stringer around the periphery of the large via.During chemical/mechanical polish, the tungsten stringer which isbounded by oxide only on one side has a tendency to lift off. Pieces oftungsten stringer may be dispersed over the surface of the die andbecome a defect problem.

Accordingly, a plurality of minimum feature size vias are formed inoxide layer 4 so that the resulting tungsten plugs (one of which isdesignated with reference numeral 14 in FIG. 2) in the vias will providea good electrical connection between the first metal plate 1 and thesecond metal plate 5 but will not have portions which tend to lift off.The remaining oxide forms a mesh-like oxide structure 15 between thefirst and second metal plates 1 and 5. Accordingly, a bond pad is formedon the same die with an amorphous silicon antifuse structure 9 having aminimum feature size tungsten plug 13.

A problem, however, exists with the structure of FIG. 2. When thestructure is encapsulated in plastic, a stress A develops between bondball 8 and oxide layer 2. Although metal plates 1 and 5 can deform torelieve the stress, oxide mesh 15 is relatively rigid and does notdeform. Consequently, stress may develop in rigid mesh 15 therebycausing cracks 16 to form in rigid mesh 15. The packaged integratedcircuit may therefore have to be discarded due to a physically impairedbond pad structure.

SUMMARY

In one embodiment, a lower conductive plate having a strip-like openingis used in a bond pad structure having conductive plugs coupling thelower conductive plate to an upper conductive plate. A volume ofrelatively rigid material filling a volume above the strip-like openingtransfers stress from the upper conductive plate, through the strip-likeopening, and to a foundation layer upon which the lower conductive plateis disposed. The bond pad structure can be fabricated using the sameprocess steps used to fabricate amorphous silicon antifuse structureshaving conductive plugs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (Prior Art) is a cross-sectional diagram of a bond pad structure.

FIG. 2 (Prior Art) is a cross-sectional diagram of an amorphous siliconantifuse structure and another bond pad structure.

FIGS. 3 and 3A are cross-sectional diagrams of a bond pad structure andan amorphous silicon anti-fuse structure in accordance with andembodiment of the present invention.

FIG. 4 is a top-down diagram of a first metal plate in accordance withone specific embodiment of the present invention.

FIG. 5 is a top-down diagram of the metal plugs of the embodiment ofFIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a cross-sectional diagram of a bond pad structure 20 and anamorphous silicon antifuse structure 21 in accordance with an embodimentof the present invention. A layer of oxide 22 is disposed on asemiconductor substrate 23. Oxide layer 22 and substrate 23 form afoundation for the bond pad structure. Although layers 22 and 23 aredisclosed here, it is to be understood that other suitable foundationsfor the bond pad may be used. The bond pad structure 20 includes a firstmetal plate 24 formed of first metalization, a plurality of tungstenplugs 25, a mesh portion 26 of an oxide layer 27 having vias into whichthe plugs are disposed, and a second metal plate 28 formed of secondmetalization. An opening is formed in a passivation layer 29 such that abond wire 30 having a bond ball 31 can be connected to the upper surfaceof the second metal plate 28.

Antifuse structure 21 includes a first signal routing lead 32 formed offirst metalization, a tungsten plug 33 disposed in a via in oxide layer27, an amorphous silicon feature 34, and a second signal routing lead 35formed of second metalization. Accordingly, the same tungstendeposition, etchback, and chemical/mechanical polishing process is usedto form the bond pad structure and the antifuse structure. Vias areformed in oxide layer 27 by reactive ion etching (RIE), tungsten isblanket CVD deposited over the entire die so that the vias are filledwith tungsten, excess tungsten is removed by etching, and the surfaceformed by oxide layer 27 and the tungsten plugs in the vias in the bondpad structure and in the antifuse structure is planarized bychemical/mechanical polishing. For additional information on the makingof the amorphous silicon antifuse structure, see U.S. patent applicationSer. No. 07/892,466, entitled “Programmable Interconnect Structures AndProgrammable Integrated Circuits”, the subject matter of which isincorporated herein by reference.

Stress can be transferred through the bond pad structure 20 from thebond ball 31 to the oxide layer 22. To prevent mesh oxide 26 from beingsubjected to large stresses that may cause mesh oxide 26 to crack, astrip-like opening is formed in the first layer of metal 24 such that anelongated strip-like volume of oxide 36 contacts both the bottom surfaceof the second metal plate 28 and the upper surface of oxide layer 22.This elongated strip-like volume of oxide is relatively wide so that itwill be strong and will not crack under a typical stress between thebond ball 31 and the underlying oxide layer 22. Accordingly, stressbetween the second metal plate 28 and the underlying oxide layer 22 istransferred through volume 36. Less stress is therefore transferredthrough the oxide mesh 26 and metal plate 24.

In some embodiments, the width D of the elongated strip-like volume ofoxide 36 is greater than distance C of oxide between adjacent plugs sothat the elongated strip-like volume of oxide will not crack under alateral stress as easily as the oxide between adjacent plugs havingseparation C. In some embodiments, the strip-like opening in the firstmetal plate 24 is larger than the width C between adjacent plugs.

In one embodiment, B is 2.0 microns, C is 1.2 microns and D is 9.6microns. The outside dimensions of first metal plate 24 are 110 by 110microns square, the tungsten plugs are 0.8 by 0.8 microns square andextend 1.0 microns in the vertical dimension. The first and second metalplates are 8,900 angstroms and 9,200 angstroms thick, respectively. Inthe embodiment of FIG. 3, first and second metal plates each includes alower titanium-tungsten layer, a middle aluminum-copper layer, and anupper titanium-tungsten layer. The amorphous silicon of the antifusestructure is deposited by plasma enhanced chemical vapor deposition(PECVD). Although the plugs of the embodiment of FIG. 3 are made oftungsten, other materials including titanium-tungsten andaluminum-copper may be used. The shapes and sizes of the vias may alsobe tailored to the particular process employed and/or the particularapplication for which the die is to be used.

FIG. 3A is a cross-sectional diagram showing second metal plate 28comprising a layer of titanium-tungsten 28A and a layer of aluminum 28B.FIG. 4 is a top-down diagram of the first metal plate in accordance withone specific embodiment of the present invention. FIG. 5 is a top-downdiagram of the metal plugs of the specific embodiment of FIG. 4. Thefirst metal plate has five strip-like openings 40-44. The centralstrip-like opening 40 has a cross-like shape. Each of the outer fourstrip-like openings 41-44 has an L-like shape. The openings are orientedsuch that the bond pad structure can transfer stress due to a bond ballforce exerted in any lateral direction. This allows the bond pad to beplaced on a die during chip layout without regard to the direction ofthe eventual stress.

Although the present invention is described in connection with certainspecific embodiments into order to illustrate the invention forinstructional purposes, the present invention is not limited to thosespecific embodiments. The present invention is not limited to use withplastic packages. Stress on parts of a bond pad susceptible to crackingmay be relieved by other than an elongated strip-like volume of oxide incontact with the foundation underlying the bond pad. The presentinvention is usable with antifuse technologies other than the tungstenplug amorphous silicon technology described herein. Conductive plugsemploying both conductive and nonconductive portions can be employed.The conductive plug of U.S. Pat. No. 5,308,795 may be employed. Theopening and/or openings in the first plate need not have a strip-likeshape but rather can have any suitable shape including squares, otherpolygons, circles and rings. In some embodiments, there are no openingsin the first plate but rather a relatively wide elongated volume ofoxide between the first plate and the second plate transfers stresswithout cracking and prevents the oxide mesh from cracking. Accordingly,various modifications, adaptations and combinations of various featuresof the various embodiments may be practiced without departing from thescope of the invention as set forth in the following claims.

What is claimed is:
 1. A bond pad structure disposed on a foundationlayer, comprising: a plurality of vertically extending conductive plugsdisposed above said foundation layer; a mesh of insulating materialdisposed around said conductive plugs; a first conductive plate disposedover said plurality of conductive plugs and said mesh of insulatingmaterial, said first conductive plate being electrically coupled to eachof said conductive plugs; a second conductive plate disposed under saidplurality of conductive plugs, said second conductive plate beingelectrically coupled to each of said conductive plugs; and means fortransferring stress from said first conductive plate to said foundationlayer, said means for transferring being disposed directly under saidfirst conductive plate, said means for transferring lying within theperiphery of said second plate.
 2. The bond pad structure of claim 1,wherein said foundation layer is a layer of oxide.
 3. The bond padstructure of claim 1, wherein said conductive plugs comprise tungsten.4. The bond pad structure of claim 1, wherein each of said conductiveplugs contacts a bottom surface of said conductive plate.
 5. The bondpad structure of claim 1, wherein said mesh of insulating material is amesh of oxide.
 6. The bond pad structure of claim 1, wherein said meansfor transferring stress from said conductive plate to said foundationlayer is a volume of said insulating material.
 7. The bond pad structureof claim 6, wherein there is a first distance between adjacent ones ofsaid plurality of vertically extending conductive plugs, said volume ofinsulating material having a width that is greater than said firstdistance.
 8. The bond pad structure of claim 6, wherein said volume ofinsulating material has an elongated strip-shaped shape.
 9. The bond padstructure of claim 6, wherein said means for transferring stress extendsto said foundation layer.
 10. A bond pad structure disposed on afoundation layer, comprising: a plurality of vertically extendingconductive plugs disposed above said foundation layer; a firstconductive plate disposed over said plurality of conductive plugs, saidfirst conductive plate being electrically coupled to each of saidconductive plugs; a second conductive plate disposed under saidplurality of conductive plugs, said second conductive plate beingelectrically coupled to each of said conductive plugs; and means fortransferring stress from said first conductive plate to said foundationlayer, said means for transferring being disposed directly under saidfirst conductive plate, said means for transferring being disposedbetween said conductive plugs, said means for transferring lying withinthe periphery of said second conductive plate, wherein said means fortransferring comprises a volume of oxide, an upper surface of saidvolume of oxide contacting a bottom surface of said first conductiveplate, a bottom surface of said volume of oxide contacting a planarupper surface of said foundation layer.
 11. The bond pad structure ofclaim 10, wherein said volume of oxide has an elongated strip-shapedshape.
 12. The bond pad structure of claim 10, further comprising a meshof oxide disposed around said conductive plugs, wherein said volume ofoxide is disposed within said mesh of oxide.